Group-III group-V compound semiconductors (often referred to as III-V compound semiconductors), such as gallium nitride (GaN) and its related alloys, have been under intense research in recent years due to their promising applications in electronic and optoelectronic devices. The large band gap and high electron saturation velocity of many III-V compound semiconductors make them excellent candidates for applications in high temperature, high voltage, and high-speed power electronics. Particular examples of potential electronic devices employing III-V compound semiconductors include high electron mobility transistors (HEMTs) and other heterojunction transistors.
Typical III-V compound semiconductor manufacturing processes use a metal lift-off technique to form metal structures. Metal is deposited over a patterned photoresist that is subsequently removed, along with any metal deposited thereon. The photoresist and metal thereon are removed in a wet etch process. Some lift-off processes employ wet etchers using batch etchants. Thus a work piece may be in contact with etchants that includes removed material from a previous work piece. Use of batch etchants mean that process control and contamination can be issues with the metal lift-off process.
In order for the metal on the photoresist to be removed, a minimum amount of photoresist has to be used. Otherwise a metal bridge may remain on the work piece. Thus, the lift-off process results in a large distance between the source and the gate that contributes to on-resistance of the device and limits the drain current.
New structures and the methods for making them that have low on-resistance and high drain current continue to be sought.